Axial flow rotary machines typically have an axially extending rotor assembly. The rotor assembly includes a rotor disk and a plurality of rotor blade assemblies extending outwardly from the disk into a working medium flow path. The gases flowing along the working medium flow path may reach temperatures in excess of 2000.degree. F. The rotor blade assemblies are bathed in the hot working medium gases. In modern engines the rotor blades of the rotor blade assemblies are cooled to increase the service life of the blade. An example of such a coolable rotor blade is shown in U.S. Pat. No. 3,994,622 entitled "Coolable Turbine Blade" issued to Schultz et al. In this blade assembly, the rotor blade is hollow and receives an impingement tube. Cooling air is flowed through the impingement tube and caused to impinge on the walls of the rotor blade to effect cooling. The cooling air is discharged typically from the trailing edge of the blade and other locations such as the leading edge region of the blade. In the Schultz et al. structure cooling air is allowed to flow between the base of the rotor blade and the impingement tube to convectively cool the shank of the blade.
In other constructions the flow path between the base of the rotor blade and the base of the impingement tube is eliminated. The base of the rotor blade is provided with a seat and the impingement tube is provided with a conforming face to provide sealing therebetween. Cooling air is flowed into the interior of the impingement tube at reduced rates and through small impingement holes in the tube to form high velocity impingement jets.